Toast walnuts at 350°F for 8–10 minutes, cool and chop.
Cream butter and sugars until light and fluffy.
Add egg, egg yolk, and vanilla. Beat to combine.
In a separate bowl, whisk flour, cornstarch, baking soda, and salt.
Add dry ingredients to wet and mix until a soft dough forms.
Fold in chocolate chips and walnuts.
Scoop dough into balls and chill for 30 minutes.
Preheat oven to 350°F. Line trays with parchment.
Bake cookies for 11–13 minutes until edges are golden.
Cool 5 minutes on tray, then transfer to wire rack.